Predictive genetic testing for adult-onset conditions, such as Huntington disease, is available to at-risk adults. Guidelines consistently recommend against such testing before adulthood unless there is associated medical benefit. Guidelines, and related commentary, cite a range of potential harms that might be associated with young people undergoing testing, yet evidence is limited. Clinical practice has forged ahead, with research demonstrating that some clinicians are making their own determinations about the best interests of individual young people and are providing testing in specific cases. For the first time, this study reports empirical evidence concerning the process and impacts of predictive testing in mature minors for adult-onset conditions where no medical benefit exists. METHODS: First-hand accounts from nine young people have been documented. All were aged 16 or 17 years of age when tested. Six tested gene positive. RESULTS: Contrary to existing assumptions, the results convey a range of benefits and absence of harms flowing from testing. Some individuals reported considerable distress associated with institutional processes before testing. CONCLUSION: The results highlight that young people from families affected by genetic conditions might possess task-specific competence relating to decision making about predictive testing. Further research and longer-term follow-up is required to study the outcomes of testing in young people.